The vast majority of dry bags are made from a lightweight flexible material such as nylon. This tends to be quite a rugged material, and it is very effective at keeping gear dry.
However, it does not provide any cushioning what so ever. Therefore when I have an item I need to keep dry and physically protect against knocks or impact shock, I tend to roll the item up in my thermals.
The Oceaner Splash Bag looks as though it might offer the best of both worlds. A dry bag that has light impact resistance.